This application claims priority of German application 199 19 434.3, filed on Apr. 29, 1999, the disclosure of which is expressly incorporated by reference herein.
The present invention relates to a transport system, particularly for the transfer of workpieces, particularly in a forming machine for massive forming.
During massive forming and also during other forming operations, workpieces frequency pass successively through several stations. The stations may, for example, be forming stations in a pressing tool, in which case the workpiece must then be transported from one station to the next. As a rule, grippers are used for this purpose to grip the parts, which may be heavy, take these parts out of a station and feed them to the next station where they release them.
A transport system of this type is described in U.S. Pat. No. 3,456,814 which has several gripper devices fastened to a holding rail. Each gripper device is constructed in the manner of tongs and has two clamping jaws which are disposed to be swivellable toward and away from one another. They form two-armed levers, one of whose lever arms is used for clamping the workpiece and the other of whose lever arms is used for the operation. For this purpose, the lever arms are connected by way of push lugs with a toothed rack whose back-and-forth movement is converted into a swivelling movement of the clamping jaws. The push lugs are arranged such that, when the clamping jaws close, they stand approximately at a right angle to the moving direction of the toothed rack. This results in a very large gearing down and vice-versa in a very high power increase toward the end of the closing movement of the clamping jaws. For operating the clamping jaws, gear wheels are used which mesh with the toothed rack and which are driven by the main press drive. The holding forces occurring at the individual workpieces are a function of the tool measurements which are subject to a certain tolerance.
Another transport system for workpieces in forming machines is described in DE 2434540 C2. Also in this system, several mechanical gripping devices are provided which are formed of two clamping jaws respectively and which are operated by a central driving source. The grippers are formed by two clamping jaws respectively formed as two-armed levers, one lever arm of which respectively being used for gripping the workpiece, and the respective other lever arm being connected with a gear wheel in an articulated manner. The gear wheels or toothed segments mesh with one another and are driven by a central drive which causes the opening and closing of all grippers. Also in this system, the control of the gripping and holding forces on the individual clamping jaws is not possible in a targeted manner.
An object of the present invention is to provide an improved transport system.
This object has been achieved by a transport system having at least one gripper device configured to grip a workpiece and having at least one movably disposed clamping jaw, and at least one driving device individually assigned to the at least one gripper device, and arranged to individually cause gripping and releasing of the workpiece of the associated at least one gripper device.
Alternatively, at least one gripper device is configured to grip a workpiece and has at least one movably disposed clamping jaw, and at least one driving device has a servomotor and a transmission configured to transmit movement applied by the servomotor to the at least one gripper device. The servomotor is configured to definably control a clamping force exercised by at least one clamping jaw onto the workpiece.
The former type of transport system has at least one, preferably several, gripper devices to which one driving device respectively is individually assigned. This means that each gripper has a separate drive. In principle, the gripping movement is therefore steerable, adjustable and controllable independently of the gripping movement of the other grippers. This permits not only a non-synchronous working of the individual grippers as required but also the controlling and steering of the gripping forces, optionally independently of component tolerances.
In the latter transport system, a servomotor is provided as a driving device. This servomotor acts upon the gripping device by way of a gearing which permits a defined power transmission. This means that, within the moving range of a clamping jaw, the ratio between the moving path of the servomotor and of the clamping jaw has a defined finite value. As a result, by way of a suitable control of the servomotor, a defined clamping force or holding force can be adjusted at the workpiece.
The servo motor is preferably connected with a position generator which is connected to a control device for controlling the gripper device. As an alternative, or in addition, the servomotor may be connected with a device for detecting the forces applied by the servomotor. This device will then also be connected with the control device. The device for monitoring the clamping force may, for example, be a force sensor on the basis of a wire strain gauge, a current sensor in a line feeding power to the servomotor, or another suitable sensor.
The transport system according to the invention permits a precision control of the movement of the clamping jaws and a precision control of the force exercised by the clamping jaws onto the workpiece. This is particularly so if the gearing has a defined power transmission characteristic without singularities as they occur, for example, in the case of toggle mechanisms. This achieves not only the adaptation of the gripping movement to possible irregularities on the workpiece which are within the production tolerance but also the control of the holding force. Thereby damage to the workpiece is avoided and a secure holding of the workpiece is nevertheless permitted.
Further, in addition to their clamping position and their opening position, the clamping jaws can take over a third position and function which is, for example, the function of guiding the workpiece without clamping it. When a gripper device holds a workpiece, for example, above a bottom die, it is possible to reduce the clamping force such that, guided by the clamping jaws, the workpiece slides through between the clamping jaws and enters the bottom die. As a result of this measure, the transport curve of the gripping device is advantageously simplified. For example, when workpieces are placed in the bottom die, it may not be necessary to move the gripper device toward the bottom die.
In a preferred embodiment, a servomotor is provided as the drive source whose rotating movement is converted by a spindle-type gearing into a linear movement. As required, however, other devices for converting rotating movements into linear movements can also be used. A roller thread spindle is preferably used which has low friction with high transmitted forces. The linear movement is preferably transmitted by way of a lever mechanism, which is, for example, only two tension lugs, to the clamping jaws. In this case, it is preferable for the tension lug with the cooperating lever arm of the clamping jaw, to enclose in approximately a right angle. In this range, the force transmission from the output of the spindle-type gearing to the clamping jaw is relatively independent of the angular position of the clamping jaw. The gear-down ratio is almost constant to promote the controllability of the gripper device.
The gripper device is preferably fastened on a holding rail together with other gripper devices. This holding rail is preferably constructed such that it bounds a closed interior space. The driving device and the gearing can be housed completely in the interior. Here, they are largely protected from damaging effects. This applies particularly with respect to a possible heat radiation emanating from the workpiece in the case of warm forming processes. As required, the interior space enclosed by the holding rail can be acted upon by compressed air, in order to prevent the penetration of disturbing substances and their advancing to the gearing, the threaded spindle and/or the servomotor.